Metal oxide catalysts containing iron, antimony and phosphorus are known to be useful in production of aldehydes by oxidation of organic compounds, production of dienes, alkenylbenzenes, unsaturated aldehydes or unsaturated acids by oxidative dehydrogenation of organic compounds, and production of nitriles by ammoxidation of organic compounds. For example, ammoxidation of propylene is described in JP-B-38-19111 (the term "JP-B" as used herein refers to an "examined Japanese patent publication"), and U.S. Pat. Nos. 3,542,843, 3,591,620 and 3,988,359; and ammoxidation of methanol is described in JP-B-54-39839, JP-A-1-143643 (corresponding to U.S. patent application Ser. No. 276,586 and European Patent Publication No 319,129Al) (the term "JP-A" as used herein refers to an "unexamined published Japanese patent application"), and U.S. Pat. Nos. 4,511,548 and 4,461,572.
The antimony-containing oxide catalysts which can be used in the reactions stated above involve problems, such as poor reproducibility and operability in the preparation thereof and difficulty in assuring high strength. As a result, some improvements have been made on a process for preparing the catalyst as described in JP-B-46-3456 and JP-B-46-3457, and U.S. Pat. Nos. 3,341,471, 3,657,155 and 3,686,138.
These conventionally proposed processes, however, do not always satisfy both activity and physical properties of the catalyst, and the problem of reproducibility of preparation still remains unsolved. In particular, in the preparation of catalysts having a high phosphorus content as in the catalyst of the present invention, direct application of conventional processes proposed for preparing antimony-containing catalysts fails to attain satisfactory results. For instance, the processes disclosed in U.S. Pat. Nos. 3,657,155 and 3,686,138 are excellent techniques for preparing iron-antimony-containing catalysts suitable for a fluidized bed process. However, it is difficult using these processes to produce catalysts containing a relatively large amount of phosphorus while retaining activity and physical properties for use in a fluidized bed process. This is assumed to be because the presence of a large amount of a phosphorus component not only inhibits oxidation of the antimony but greatly changes the properties of the slurry reducing its stability.
The present inventors had previously found that the activity and physical properties of the catalyst can be improved by adjusting the pH of a slurry during the preparation of the catalyst to not higher than 3 before spray drying when a relatively large amount of phosphorus component is used as a part of raw materials for the catalyst. An improved process described in JP-A-1-171640 (corresponding to European Patent Publication No. 323,129Al) was proposed.
However, it has been found that the proposed process has disadvantages in that a specific component, particularly antimony oxide in the slurry settles out readily, the properties of the slurry are easily changed with the passage of time, the slurry is deposited on the wall of a chamber during spray drying and it is difficult to remove the deposit. Further, the operability during the preparation of the catalyst is poor, for example, the catalyst readily adheres to the vessel during the calcination of the catalyst. In addition, the reproducibility of the catalyst remains unsatisfactory. Particularly, the margin of manufacturing conditions capable of producing a catalyst having physical properties suitable for a fluidized bed reaction is relatively narrow, and the physical properties of the catalyst are greatly varied by a slight change in the preparation conditions of the slurry or in the spray drying conditions of the slurry. Accordingly, the above-described process is not considered to be fully suitable for practical use.
Since the industrial output of products obtained by the oxidation or ammoxidation of organic compounds is high, a slight increase in the yields of the desired products or a slight improvement in the physical properties of the catalyst or catalyst strength gives remarkable commercial and economic effects.
This invention has been performed to improve the activity and physical properties of a catalyst containing iron, antimony and a large amount of phosphorus.